<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    /* 交集选择器 */
    /* div 元素 + box class */
    div.box {
      color: rgb(0, 255, 255);
    }
  </style>
</head>

<body>
  <div class="box">我是div元素</div>
  <p class="box">我是p元素</p>
</body>

</html>